Chances are someone you know has had skin cancer at some point in his or her lifetime. In fact, skin cancer is the most common form of human cancers, affecting more than two million Americans each year, according to the American Cancer Society.

Skin cancers are generally curable if caught early, which is why regular self-examination and medical checkups are important.

The vast majority of skin cancers are composed of three different types: basal cell carcinoma, squamous cell carcinoma and melanoma.

Basal Cell Carcinoma

This is the most common form of skin cancer, often occurring on the face or neck. Basal cells reside in the deepest layer of the skin. Overexposure to UVB radiation damages the body’s natural repair system, which causes basal cell carcinomas to grow. These tend to be slow-growing tumors and rarely spread. They can appear as:

Basal cell carcinoma risk factors include having fair skin, sun exposure, older age, exposure to UV radiation such as in tanning beds, and therapeutic radiation given to treat an unrelated health issue.

Squamous Cell Carcinoma

These cells are found in the upper layer of the skin and appear as a crusted or scaly patch of skin with an inflamed, red base.

Squamous cell carcinoma can develop anywhere, but most frequently appear on the scalp, face, ears and back of hands. Squamous cell carcinoma is most prevalent among fair-skinned, middle-aged and elderly people who have a history of sun exposure.

Melanoma

Melanoma is the least common type of skin cancer, but the most dangerous. Melanocytes are cells found in the bottom layer of the skin and produce melanin, which is responsible for skin pigmentation. Melanoma is presented as dark brown or black spots on the skin and can spread rapidly to internal organs and the lymph system. Melanomas look like moles and often do grow inside existing moles. That’s why it is important for people to conduct regular self-examinations of their skin, as early detection is critical for curing melanoma.

Most melanomas are caused by overexposure to the sun beginning in childhood. Melanoma is the most common form of cancer among young adults age 25 to 29.